1. Field of the Invention
The present invention relates to an optical functional device utilizing a slab-type and two-dimensional photonic crystal.
2. Related Art Statement
An optical device utilizing a photonic crystal has a structure of repeating different two kinds of dielectric materials having different dielectric constants. According to such devices, the internal multiple reflection phenomenon is utilized to provide various kinds of devices having superior functions and of very small sizes. Since the principle of function of the device is based on multiple reflection phenomenon, the device properties have a strong dependency on frequency (wavelength) in the vicinity of a specific frequency. The frequency is decided upon the material (refractive index N) of a substrate for a photonic crystal and a length d of period of repetition of the photonic crystal structure. The dependency of the device on frequency is characteristic to the device. However, in the case that the device is used in a wide range of wavelength, the characteristics would turn to be a defect.
An optical waveguide utilizing a slab-type and two-dimensional photonic crystal is described, for example, in the following documents.
Japanese patent publication No. 2005-172932A
Japanese patent publication No. 2003-156642A
Japanese patent publication No. 2005-70163A
Japanese patent publication No. 2002-350657A
Further, according to “IEEE PHOTONICS TECHNOLOGY LETTERTS” VOL. 17, No. 10, October 2005, pages 2083 to 2085, “Thermooptic Switch Based on Photonic-Crystal Line-Defect Waveguides”, an optical waveguide of Mach-Zehnder type is formed in a slab type two-dimensional photonic crystal, as shown in FIG. 1. This device is of SOI type, ands its slab type two dimensional photonic crystal, insulating layer (buffer layer) and supporting body are made of silicon.
Further, it is disclosed a device of SOI type in “Applied Physics” vol. 74, No. 2 (2005), pages 147 to 158, “Recent progresses and future prospects of two-dimensional and three-dimensional photonic crystals” by Susumu NODA. According to this device, a slab-type and two-dimensional photonic crystal is provided on a silicon wafer through a buffer layer of silicon dioxide. A space is formed direct under a waveguide portion (See FIG. 3). This is not an optical modulator of Mach-Zehnder type.
For example, it is expected to realize a high-speed optical functional device by forming a traveling type electrode in a two-dimensional and trianglular lattice photonic crystal and inputting a high frequency signal onto the electrode from the outside.